Deposition of metal borides

ABSTRACT

A method for depositing a metal film onto a substrate is disclosed. In particular, the method comprises pulsing a metal halide precursor onto the substrate and pulsing a decaborane precursor onto the substrate. A reaction between the metal halide precursor and the decaborane precursor forms a metal film, specifically a metal boride.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. Non-Provisional patent application Ser. No. 15/135,224, filed Apr. 21, 2016 and entitled “DEPOSITION OF METAL BORIDES” and U.S. Non-Provisional application Ser. No. 15/135,258, filed Apr. 21, 2016 and entitled “DEPOSITION OF METAL BORIDES AND SILICIDES,” the disclosures of which are hereby incorporated by reference in their entireties.

FIELD OF INVENTION

The present disclosure generally relates to processes for manufacturing electronic devices. More particularly, the disclosure relates to forming metal gates through atomic layer deposition (ALD). Specifically, the disclosure relates to forming metal metal borides with decaborane.

BACKGROUND OF THE DISCLOSURE

Metal boride films have been formed using various chemical vapor deposition (CVD) methods. In the CVD methods, gaseous source chemicals are introduced into a reaction space at the same time, resulting in a deposition of a metal film on the substrate. In order to thermally activate some of the gaseous source chemicals, the CVD methods tend to take place at temperatures as high as 1200° C. The high substrate temperatures relative to thermal budgets may be problematic, especially for state-of-the-art semiconductor fabrication processes such as metallization.

In addition, physical vapor deposition (PVD) methods have also been used to deposit metal films. PVD methods generally deposit along a line-of-sight. However, line-of-sight deposition results in insufficient thin film coverage in certain areas where complex substrate contours are involved. Also, line-of-sight deposition results in low-volatility precursors depositing on the first solid surface encountered, leading to low-conformality coverage.

Atomic layer deposition (ALD) has been used to form metal carbide films. For example, U.S. Pat. No. 7,611,751 to Elers discloses methods for forming a metal carbide film through spatially and temporally separated vapor phase pulses of a metal source chemical, a reducing agent, and a carbon source chemical. Similarly, U.S. Pat. No. 8,841,182 to Chen et al. discloses the formation of titanium carbide films through an ALD process. However, no known ALD solution exists to deposit metal boride at low temperatures using decaborane. As a result, a method using ALD to form metal borides at low temperatures is desired.

SUMMARY OF THE DISCLOSURE

In accordance with at least one embodiment of the invention, a method for forming a metal boride is provided. The method comprises: providing a substrate for processing in a reaction chamber; performing a metal precursor deposition onto the substrate, the performing the metal precursor deposition step comprises: pulsing a metal precursor onto the substrate; and purging an excess of the metal precursor from the reaction chamber; and performing a decaborane precursor deposition onto the substrate, the performing the decaborane precursor deposition step comprises: pulsing a decaborane precursor onto the substrate; and purging an excess of the decaborane precursor from the reaction chamber; wherein the metal precursor comprises one of: titanium tetrachloride (TiCl₄), niobium pentachloride (NbCl₅), tantalum pentafluoride (TaF₅), and niobium pentafluoride (NbF₅); wherein a reaction between the metal halide precursor and the decaborane precursor forms a film comprising at least one of: titanium boride (TiB), tantalum boride (TaB), or niobium boride (NbB); wherein the metal precursor deposition step is repeated a predetermined number of times; and wherein the decaborane precursor deposition step is repeated a predetermined number of times.

In accordance with at least one embodiment of the invention, a method for forming a metal boride is provided. The method comprises: providing a substrate for processing in a reaction chamber; exposing the substrate to a metal halide precursor; exposing the substrate with a purge gas after exposing the substrate to the metal halide precursor; exposing the substrate to a decaborane precursor; exposing the substrate with the purge gas after exposing the substrate to the decaborane precursor; wherein the metal halide precursor exposing step is repeated a predetermined number of times; and wherein the decaborane precursor exposing step is repeated a predetermined number of times.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the invention disclosed herein are described below with reference to the drawings of certain embodiments, which are intended to illustrate and not to limit the invention.

FIG. 1 is a flowchart of a method in accordance with at least one embodiment of the invention.

FIG. 2 is a flowchart of a step in accordance with at least one embodiment of the invention.

FIG. 3 is a flowchart of a step in accordance with at least one embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below.

Metal boride films demonstrate potential use in a myriad of applications due to their characteristics. For example, these metal films have a low work function and low resistivity, which make such films ideal for n-metal gate or gate fill applications. Also, the high chemical resistance of metal borides makes them applicable for use in patterning layers and hard masks. Furthermore, the high work function and low resistivity of metal films provide for applicability in p-metal stack, gate fill, and MIMCAP electrodes (SoC).

Metal borides may be used in several applications. For example, due to their low resistivity, metal borides may serve as contacts, electrodes, or barriers. Metal borides may also be used in PMOS metal gate applications, where a work function may exceed 4.9 eV or range between approximately 5.0 eV and 5.2 eV at approximately a 3 nm thickness. A resistivity of approximately 100 μΩcm at thicknesses of approximately 10 nm may be achieved. In addition, metal borides may also be used in NMOS metal gate applications, where a work function may be less than approximately 4.3 eV or range between 4.1 eV and 4.2 eV at approximately a 3 nm thickness. A resistivity less than approximately 300 g/cm at thicknesses of approximately 10 nm may be achieved. Metal borides may serve as conductive layers in integrated circuits, where the resistivity may be less than about 5000 μΩcm, less than about 2000 μΩcm, less than about 1000 μΩcm, less than about 500 μΩm, or less than about 250 μΩm.

Decaborane (B₁₀H_(x)), for example B₁₀H₁₄, is a precursor with ten boron atoms, which is greater than that of diborane (B₂H₆). Thus, there are marked differences between decaborane and diborane in properties when used as precursors to form metal borides. For example, decaborane is a solid at room temperature, making it easier to handle. On the other hand, diborane is a gas at room temperature. The fact that decaborane is a solid makes it much easier to handle, and safer as there is a lessened risk of explosion in comparison to diborane. In addition, depending on conditions and residence times, decaborane may start to decompose at temperatures exceeding 300° C., 350° C., 375° C., or 400° C. This factor may factor into setting a temperature for the reaction chamber.

FIG. 1 illustrates a method for depositing a metal gate in accordance with at least one embodiment of the invention. The method includes a metal precursor pulse/purge step 100 and a decaborane pulse/purge step 200. The steps take place within a reaction chamber of an atomic layer deposition device. Such a device may include an EmerALD® XP ALD process module from ASM International N.V. Within the reaction chamber, a substrate to be processed is placed. The substrate may be made of silicon oxide (SiO₂), silicon (Si), silicon germanium (SiGe), germanium (Ge), gallium arsenide (GaAs), or indium phosphide (InP). The substrate surface may also have a film of titanium nitride (TiN), titanium oxide (TiO₂), hafnium oxide (HfO₂), silicon oxide (SiO₂), low-k SiO₂, or aluminum oxide (Al₂O₃). The substrate surface may also comprise other high-k films or conductive films comprising nitride, transition metal nitrides, carbides, silicides, or mixtures thereof.

The metal precursor pulse/purge step 100 may be repeated after a previous metal halide pulse/purge step via a pathway 300. Similarly, the decaborane pulse/purge step 200 may be repeated after a previous decaborane compound pulse/purge step via a pathway 310. In addition, the whole process may be repeated via a pathway 320. Such may be desirable in order to form a metal boride film of a desired thickness. For example, 50 cycles of the metal precursor pulse/purge step 100 and 50 cycles of the decaborane compound pulse/purge step 200 may result in the formation of a metal boride film with a thickness of 200 Angstroms.

It is possible that some decomposition of the boron compounds may occur, for example, if the reaction temperature is selected such way that slight decomposition is possible. In particular embodiments, more than a monolayer of boron compound is adsorbed to surface. In other embodiments, more than a monolayer of boron compound is adsorbed to surface, which is then further reacted with the metal halide to form metal boride. In some embodiments, the metal boride film is formed with ALD type of process. In some embodiments, the boron reaction to surface may not be self-limiting to one monolayer due to decaborane decomposition. In some embodiments, the sequential process may not be an ALD process, but instead a sequential CVD process, for example. In some embodiments, one or more of the purge step(s) may be omitted and replaced by evacuation or removing step steps without the use of inert gas. In some embodiments, one or more of the purge step(s) may be replaced by flowing small concentration of (deca)borane precursor with or without inert gas. In some embodiments, the decaborane reaction or metal halide reaction may not form a layer; instead, what may be formed may be isolated locations of material or islands, possibly separate or partially connected, of material comprising boron or metal halide, respectively.

FIG. 2 illustrates steps of the metal precursor pulse/purge step 100. The metal precursor pulse/purge step comprises a metal precursor pulse 110 and an inert gas purge 120. Metal halides may be used in the metal precursor pulse 110, such as, for example, titanium tetrachloride (TiCl₄), niobium pentachloride (NbCl₅), niobium pentafluoride (NbF₅), titanium tetrafluoride (TiF4), titanium tetrachloride (TiCl4), or tantalum pentafluoride (TaF₅). Other metal halides in the metal precursor pulse 110 may include: a transition metal fluoride; Group IV-VI halides; group IV fluorides; or fluorides of tantalum (TaF_(x)), titanium (TiF_(x)), or niobium (NbF_(x)). During the metal precursor pulse 110, metal halides may be introduced into the reaction chamber through a showerhead precursor delivery system and be incident on the substrate. The metal halide may interact with active sites on the substrate to form a monolayer film of metal halide.

In order to get optimal film formation, there may be optimal settings to run the process. For example, the metal halide may be kept at temperature ranging between 50 and 120° C., preferably between 90 and 100° C. or preferably between 50 and 70° C., prior to entering into the reaction chamber. The temperature within the reaction chamber during the metal halide pulse 110 may range between 350 and 450° C., preferably between 370 and 400° C., which may prove to be beneficial as providing a low thermal budget. In addition, the pressure within the reaction chamber during the metal halide pulse 110 may be between 0.1 to 10 Torr. Each metal halide pulse 110 may take between 0.1 and 5 seconds, preferably between 0.5 and 1 second.

The inert gas purge 120 serves the purpose of removing any excess metal halide precursor introduced into the reaction chamber during the metal precursor pulse step 110. Inert gases that may be used during the inert gas purge 120 include nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), or other rare gases.

FIG. 3 illustrates the decaborane pulse/purge step 200 in accordance with at least one embodiment of the invention. The decaborane pulse/purge step 200 includes a decaborane pulse 210 and an inert gas purge 220.

The decaborane pulse 210 involves a pulsing of a decaborane compound. When the decaborane pulse 210 commences, the substrate in the reaction chamber may have a monolayer of a metal halide operating as active sites for decaborane. For example, the substrate may have a layer of niobium pentafluoride when a pulse of decaborane is introduced into the reaction chamber. Without disclaiming any theory, it is believed that the decaborane reacts with the niobium pentafluoride according to the following equation in order to form a pure niobium boride film: NbF₅+B₁₀H₁₄→NbB₂+HF+H₂

The formation of pure niobium boride or pure titanium boride films is advantageous due to properties of oxidation resistance, high chemical resistance, high stiffness and low resistivity in proper phase, for example. It has great applicability in, for example, patterning layers, hard masks, back-end-of-line (BEOL) interconnects, gate barriers, contacts, electrode, or gate fills. These films may also be used in integrated circuits, MEMS, microelectronics, or protective coatings.

Similar to the metal halide pulse 110, in order to get optimal film formation, there may be optimal settings to run the decaborane pulse 210. For example, the decaborane compound may be kept at a temperature not exceeding 65° C., preferably not exceeding 55° C., prior to entering into the reaction chamber. The temperature within the reaction chamber during the decaborane pulse 210 may be greater than 300° C., 350° C., 375° C., or 400° C. or range between 300 and 500° C., preferably between 350 and 450° C., which allows for a low thermal budget. In addition, the pressure within the reaction chamber during the decaborane pulse 210 may be between 0.1 to 10 Torr, preferably between 0.5 to 5 Torr. Each decaborane compound pulse 210 may take between 0.05 and 20 seconds, preferably between 0.5 and 10 seconds.

The inert gas purge 220 serves the purpose of removing any excess borane compound precursor introduced into the reaction chamber during the decaborane compound pulse step 210. Inert gases that may be used during the inert gas purge 220 include nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), or other rare gases.

As a result of the cycling, a titanium boride or a niobium boride film may be formed. The film may include a metal-boride bond. On the other hand, the film may include a metal and boron trapped inside the film without a true metal-boride bond. The resulting film may be used in a MOS application, for example. The film may include elements having the following atomic concentrations: (1) Boron from about 30 to about 80%, preferably from about 40 to about 80%, and more preferably from about 50 to about 70%; (2) Metal from about 20 to about 70%, preferably from about 20 to about 60%, and more preferably from about 30 to about 50%; (3) Oxygen having less than about 5%, preferably less than 1%; (4) Hydrogen having less than about 5%, preferably less than 1%; and (5) Fluorine having less than about 5%, preferably less than 1%.

In accordance with at least one embodiment of the invention, a metal boride growth rate ranging between 0.05 and 8 Å/cycle may be achieved. For example, the growth rate may be more than 0.05 Å/cycle, more than about 0.5 Å/cycle, more than about 1.0 Å/cycle, or more than about 1.5 Å/cycle. The growth rate may also be less than about 8 Angstroms per cycle, less than about 6 Å/cycle, less than about 5 Å/cycle, or less than about 4 Å/cycle. A growth rate exceeding 10 Angstroms per cycle may be achieved, but would require an exceedingly high temperature of the reaction chamber.

In accordance with at least one embodiment of the invention, formation of niobium boride by niobium pentafluoride and decaborane may have a variable growth rate. In particular, the growth rate of niobium boride may vary depending on the pulse duration of both the decaborane and the niobium pentafluoride. The growth rate may be increased if there is longer dosage duration of decaborane, while the growth rate may be decreased if there is longer dosage duration of the niobium pentafluoride. In addition, the niobium boride film formed may primarily comprise NbB₂, with an undetectable amount of fluorine in the film.

In accordance with at least one embodiment of the invention, formation of niobium boride may occur with pulses of niobium pentachloride and decaborane. The niobium boride film formed may be amorphous and non-conductive. A low reactivity between chlorides and decaborane may result in a lower growth rate or higher boron content.

In accordance with at least one embodiment of the invention, formation of titanium boride may occur with pulses of titanium tetrachloride and decaborane.

The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the aspects and implementations in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationship or physical connections may be present in the practical system, and/or may be absent in some embodiments.

It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. Thus, the various acts illustrated may be performed in the sequence illustrated, in other sequences, or omitted in some cases.

The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems, and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof. 

We claim:
 1. A method of forming a film having a metal boride comprising: providing a substrate for processing in a reaction chamber; performing a metal precursor deposition onto the substrate, the performing the metal precursor deposition step comprises: pulsing a metal precursor onto the substrate; and purging an excess of the metal precursor from the reaction chamber; and performing a decaborane precursor deposition onto the substrate, the performing the decaborane precursor deposition step comprises: pulsing a decaborane precursor onto the substrate, wherein prior to entering into the reaction chamber, the decaborane precursor is kept at a temperature not exceeding 65° C.; and purging an excess of the decaborane precursor from the reaction chamber; wherein the metal precursor comprises one of: titanium tetrachloride (TiCl₄), niobium pentachloride (NbCl₅), tantalum pentafluoride (TaF₅), and niobium pentafluoride (NbF₅) and wherein prior to entering the reaction chamber, the metal halide is kept at temperature ranging between 50° C. and 120° C.; wherein a reaction between the metal halide precursor and the decaborane precursor forms a film comprising at least one of: titanium boride (TiB), tantalum boride (TaB), or niobium boride (NbB); wherein the metal precursor deposition step is repeated a predetermined number of times; and wherein the decaborane precursor deposition step is repeated a predetermined number of times.
 2. The method of claim 1, wherein a temperature of the reaction chamber is greater than 300° C.
 3. The method of claim 2, wherein the temperature of the reaction chamber is greater than 375° C.
 4. The method of claim 1, wherein a pressure of the reaction chamber ranges between 0.1 and 10 Torr.
 5. The method of claim 1, wherein the pulsing the metal precursor has a duration of 0.1 and 5 seconds.
 6. The method of claim 1, wherein the pulsing the decaborane precursor has a duration of 0.05 and 20 seconds.
 7. The method of claim 1, wherein purging the excess of the metal precursor comprises purging the reaction chamber with at least one of: nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), or other rare gases.
 8. The method of claim 1, wherein purging the excess of the decaborane precursor comprises purging the reaction chamber with at least one of: nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), or other rare gases.
 9. The method of claim 1, wherein the film has a concentration of Boron from about 30 to about 80 at. %.
 10. The method of claim 1, wherein the film has a concentration of a metal from about 20 to about 70 at. %.
 11. The method of claim 1, wherein the film has a concentration of Oxygen of less than 5 at. %.
 12. The method of claim 1, wherein the film has a concentration of Hydrogen of less than 5 at. %.
 13. The method of claim 1, wherein the film has a concentration of a halide of less than 5 at. %.
 14. A method of forming a film having a metal boride comprising: providing a substrate for processing in a reaction chamber; exposing the substrate to a metal halide precursor, wherein prior to entering the reaction chamber, the metal halide is kept at temperature ranging between 50° C. and 120° C.; exposing the substrate with a purge gas after exposing the substrate to the metal halide precursor; exposing the substrate to a decaborane precursor, wherein prior to entering into the reaction chamber, the decaborane precursor is kept at a temperature not exceeding 65° C.; and exposing the substrate with the purge gas after exposing the substrate to the decaborane precursor; wherein the metal halide precursor exposing step is repeated a predetermined number of times; and wherein the decaborane precursor exposing step is repeated a predetermined number of times.
 15. The method of claim 14, wherein the purge gas comprises at least one of: nitrogen (N₂), argon (Ar), helium (He), hydrogen (H₂), or other rare gases.
 16. The method of claim 14, wherein a temperature of the reaction chamber is greater than 300° C.
 17. The method of claim 16, wherein the temperature of the reaction chamber is greater than 375° C.
 18. The method of claim 14, wherein exposing the substrate to the metal halide precursor comprises pulsing the metal halide precursor.
 19. The method of claim 14, wherein exposing the substrate to the decaborane precursor comprises pulsing the decaborane precursor.
 20. The method of claim 14, wherein exposing the substrate to the purge gas comprises pulsing the purge gas. 